Note that if you would have typed whatever you wanted instead, it probably would have worked as long as the first was "corrected".
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GnoupiMay 5 '10 at 13:09

16

How do we know that you're human unless you pass the CAPTCHA? Everyone be on your guard!! "Code Poet" is a human impersonator! He's trying to enlist your help to beat the CAPTCHA!
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devinbMay 5 '10 at 13:15

11

to add to Gnoupi's answer, SO uses re-captcha one of the words is known and one of the words is a scan from an old book. By giving the captcha to many people, they can accurately determine the scanned words the computer can't recognize. Effectively using small amounts of peoples time as powerful computer power to electronify books.
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LumpyMay 5 '10 at 13:18

@Lumpy - if your comment had a checkmark next to it, it would be marked check.
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Sky SandersMay 5 '10 at 13:44

8

As designed. A robot would not head off to meta, post this question, learn how to enter the CAPTCHA, then return to the page and complete the challenge. So clearly you are not a robot, and the CAPTCHA worked!
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Craig StuntzMay 5 '10 at 15:07

16 Answers
16

Each new word that cannot be read correctly by OCR is given to a user in conjunction with another word for which the answer is already known. The user is then asked to read both words. If they solve the one for which the answer is known, the system assumes their answer is correct for the new one.

So therefore if nobody else figured out this one, you would be the first and you could legitimately type anything and succeed at it.

@code poet: Yes. In linux there is a very handy app that allows you to access all symbols.
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Martijn CourteauxMay 5 '10 at 13:10

19

NULL SET and PHI are not the same glyph.
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quack quixoteMay 5 '10 at 13:25

1

@Quack Quixote: correct, the correct glyph is U+03D5 Greek Phi Symbol (referring to the posted image, it is the incorrect glyph). Windows also has a character lookup, called the Character Map.
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JoshuaMay 5 '10 at 13:38

&phi; doesn't work though :) it's clearly the capital letter Phi: ɸ. I am not sure of the HTML code for that though.
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JoshuaMay 5 '10 at 13:49

7

@Joshua: The capital Greek Phi (&Phi;) is Φ (U+03A6), not ɸ which is the Cyrillic Ef (U+0444). There's also a phi symbol ϕ (U+03D5) which may render like the image, depending on the font.
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kennytmMay 5 '10 at 13:54

You know, providing LaTeX equations in captchas would be excellent for mathoverflow.com to keep out the riff-raff. They're always complaining that they get too many elementary-level questions there... ;)
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EtherMay 5 '10 at 14:49

Nice. And odd that they know where to find the number, but then still need a human to confirm its value ;-)
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ArjanMar 28 '12 at 5:47

4

I've seen this recently. No else that I know agreed with me, about those being house numbers though. I am so happy that there is some else who believes that they are house numbers too!
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Ellie KesselmanAug 8 '12 at 20:24